2023 L8T 10 Speed

newdude · December 18, 2021

ALSO.

For comparison, here's TFL's run with the Ford 7.3 gas and 10 speed. Both engines make similar power, the Ford ran the test configured with 4.30 gearing.

newdude · December 18, 2021

At a minimum, GM needs to do 10L90 with 3.73.

Ideally, they should do 10L90 and 4.10. The 10 speed has low enough OD gears to get good mileage still and shouldn't be a problem.

Don't forget, these T1 HD are much heavier than their K2 counterparts. A T1 regular cab 1 ton has almost the same curb weight as a K2 2500hd double cab. Gas crew cabs come in 7000-7300lbs depending on options.

Edited December 18, 2021 by newdude

Ray Pickle · December 18, 2021

1 hour ago, newdude said:

ALSO.

For comparison, here's TFL's run with the Ford 7.3 gas and 10 speed. Both engines make similar power, the Ford ran the test configured with 4.30 gearing.

What TFL comparison clearly indicates is poor programing algorithm of transmission mapping. Any experienced driver would never allow engine to lug like they dis in the test. For uniformity of testing I understand why they did it, but it in no way reflects how the truck would perform driven properly with its power band.

MTU Alum · December 18, 2021

1 hour ago, Ray Pickle said:

What TFL comparison clearly indicates is poor programing algorithm of transmission mapping. Any experienced driver would never allow engine to lug like they dis in the test. For uniformity of testing I understand why they did it, but it in no way reflects how the truck would perform driven properly with its power band.

Unless the engine is telling it not to shift. Things are not always as they seem.

#iworkforGM

Ray Pickle · December 18, 2021

Curious what that means?

Another JR · December 18, 2021

Me too. You always have the option to force it to 4th or lower by shifting to L. At least that’s what the manual says.

MTU Alum · December 18, 2021

59 minutes ago, Another JR said:

Me too. You always have the option to force it to 4th or lower by shifting to L. At least that’s what the manual says.

ECM can deny manual downshifts as well.

Ray Pickle · December 18, 2021

6 minutes ago, MTU Alum said:

ECM can deny manual downshifts as well.

However to your intial comment- the engine cannot. Further the ecm is by not commanding the downshift is in fact defacto denying it. The programming is the issue- I have towed the "ike" more than once and in similiar weather variables to the test conditions along with warmer days and have never been denied a downshift. Surprisingly the truck would hold 2nd gear at redline if I desired on the steepest sections or slowly lose speed and rpm ascending in 3rd towing 12k 5vr. Trans temp would creap as you would expect if I beat it like that so I choose not to. But neither trans nor coolant temps went anywhere near the danger zone. I typically choose to tow it at a more drivetrain friendly 40 mph ish range.

vucelick · December 19, 2021

9 hours ago, newdude said:

10L90 from the ZL1 is the most likely candidate. 10L1000 would be overkill and un-necessary behind the 6.6 gas. Much larger and heavier, needs more input power (duramax) to spin everything.

ZL1 2012-2015 used the 6L90 from the HD so to me it only makes sense.

The allison 1000 was used behind the 8.1l big block gas motor and the diesel. The new 6.6 is similar in power to the older big block, i believe the 10/1000 is more than appropriate for the 6.6's power.

MTU Alum · December 19, 2021

5 hours ago, Ray Pickle said:

However to your intial comment- the engine cannot. Further the ecm is by not commanding the downshift is in fact defacto denying it. The programming is the issue- I have towed the "ike" more than once and in similiar weather variables to the test conditions along with warmer days and have never been denied a downshift. Surprisingly the truck would hold 2nd gear at redline if I desired on the steepest sections or slowly lose speed and rpm ascending in 3rd towing 12k 5vr. Trans temp would creap as you would expect if I beat it like that so I choose not to. But neither trans nor coolant temps went anywhere near the danger zone. I typically choose to tow it at a more drivetrain friendly 40 mph ish

You have your opinion and I have mine. Mine is based on running grades with powertrain calibrators. The heat rejection is high on this L8T and you have to control it eventually by keeping the rpms lower by commanding upshifts, denying downshifts, and/or pulling spark.

Another JR · December 19, 2021

So can it be seen from coolant temp or transmission temp when the ecm will prevent downshifts?

C/K Man · December 19, 2021

3 hours ago, MTU Alum said:

You have your opinion and I have mine. Mine is based on running grades with powertrain calibrators. The heat rejection is high on this L8T and you have to control it eventually by keeping the rpms lower by commanding upshifts, denying downshifts, and/or pulling spark.

I have heard that the heat rejection of the L8T is high, and I have been wondering if that's been keeping it out of the Silverado 4500/5500/6500. Then again I see that the L8T is now in some of the Isuzu based LCF's with GVW's approching 15,000#'s, so one would think the L8T ought to be O.K. at least for the Silverado 4500's.

BTW, I have a hunch that the heat rejection of the L8T is at least better than the Ford 7.3L Godzilla.........

Another JR · December 19, 2021

Personally I’m glad if GM has included a feature to protect from overheat damage. I’d just like to understand it and know how to avoid getting the truck into that condition in the first place.

That TFL video showing them starting and continuing a long, high altitude steep climb in warm conditions (or any weather for that matter) with a maximum trailer load in terms of both weight and aerodynamic drag by just holding the pedal to the floor is not how anyone who cares about their equipment would drive. (Yes, i understand their intent was to provide a comparison. ) Personally, I would find a speed that could be held with the engine between 3000 and 4000 rpm on the grade, and I would climb at that speed if it was safe for the road conditions.

I’m curious to know if the truck would have a problem with that technique on that Ike climb, and that’s the test that would have been meaningful to me (what speed can it hold on that climb) when deciding on a truck. However, even that test would not be critical to me because I don’t ever expect to tow with more than 10k and have no reason to tow a heavy boat over the Rockies. I understand it may be important to those with other trailering needs.

Ray Pickle · December 19, 2021

1 hour ago, Another JR said:

Personally I’m glad if GM has included a feature to protect from overheat damage. I’d just like to understand it and know how to avoid getting the truck into that condition in the first place.

That TFL video showing them starting and continuing a long, high altitude steep climb in warm conditions (or any weather for that matter) with a maximum trailer load in terms of both weight and aerodynamic drag by just holding the pedal to the floor is not how anyone who cares about their equipment would drive. (Yes, i understand their intent was to provide a comparison. ) Personally, I would find a speed that could be held with the engine between 3000 and 4000 rpm on the grade, and I would climb at that speed if it was safe for the road conditions.

I’m curious to know if the truck would have a problem with that technique on that Ike climb, and that’s the test that would have been meaningful to me (what speed can it hold on that climb) when deciding on a truck. However, even that test would not be critical to me because I don’t ever expect to tow with more than 10k and have no reason to tow a heavy boat over the Rockies. I understand it may be important to those with other trailering needs.

It will easily hold 3 to 4500 rpm up the ike with more weight than you describe. Further the engine/cooling system will be happier in that range than lugging it and beating the bearings out of it as a result.

ShotgunZ71 · December 19, 2021

1 hour ago, Another JR said:

That TFL video showing them starting and continuing a long, high altitude steep climb in warm conditions (or any weather for that matter) with a maximum trailer load in terms of both weight and aerodynamic drag by just holding the pedal to the floor is not how anyone who cares about their equipment would drive. (Yes, i understand their intent was to provide a comparison. ) Personally, I would find a speed that could be held with the engine between 3000 and 4000 rpm on the grade, and I would climb at that speed if it was safe for the road conditions.

I’m curious to know if the truck would have a problem with that technique on that Ike climb, and that’s the test that would have been meaningful to me (what speed can it hold on that climb) when deciding on a truck. However, even that test would not be critical to me because I don’t ever expect to tow with more than 10k and have no reason to tow a heavy boat over the Rockies. I understand it may be important to those with other trailering needs.

My experience when I had the L8T was similar to what you say. The grades I climbed, albeit Blue Ridge/Smokey Mountains, the truck never had an issue keeping speed on grades when the RPM stayed between 3000-4000 RPMs. Honestly, closer to 4k and you could really tell it was in the sweet spot. I have no doubt that the engine could keep at this RPM for hours on end with no issues.

I'd like to add that I was pulling a 15k lb 5th wheel (parachute) doing these climbs. Engine and transmission temps actually cooled due to the higher RPM and less lugging on the engine. Fuel economy was also slightly better with the higher RPM (on flatter ground, not during the climb)in most cases.

Edited December 19, 2021 by ShotgunZ71